Mask



FIG. 1 is a front isometric view of a mask;

FIG. 2 is a rear isometric view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a left side view thereof;

FIG. 7 is a right side view thereof; and,

FIG. 8 is a rear view thereof.

The broken lines illustrate a strap represent an environment and form no part of the claimed design, and the remaining broken lines illustrate portions of the mask that form no part of the claimed design. 

CLAIM The ornamental design for a mask, as shown and described. 